Multilayer laminate wound dressing

ABSTRACT

A flexible, multilayer wound dressing with antibacterial and antifungal properties, together with methods for making the dressing. The dressing includes a layer of silver-containing fabric, a layer of absorbent material, and (optionally) a layer of flexible air-permeable and/or water-impermeable material. The dressing can be used for prophylactic and therapeutic care and treatment of skin infections and surface wounds (including surgical incisions), as a packing material, and as a swab for surface cleaning.

This application is a continuation of pending prior U.S. applicationSer. No. 11/220,566 filed Sep. 6, 2005, which is a divisional of U.S.Ser. No. 08/707,779 filed Sep. 3, 1996, which is a continuation-in-partof application Ser. No. 08/524,134, filed Sep. 5, 1995 and 08/623,046filed Mar. 28, 1996, now U.S. Pat. No. 5,814,094.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a multilayer dressing for the care andtreatment of wounds. In particular, the present invention relates to amultilayer dressing having therapeutic and prophylactic properties, andmethods for making the dressing.

2. Discussion of Background

The antimicrobial and antifungal properties of silver and silvercompounds are well known. Topical preparations that contain silver orsilver compounds—silver nitrate solution, silver sulfadiazine cream,colloidal silver compositions, silver-protein compounds such as Agyrol™,and so forth—are widely used in medicine. The useful effects of thesecompositions are due to the small amounts of free silver ions producedby dissociation of the silver compound or to formation of toxicby-products in situ.

The effectiveness of silver as an antimicrobial agent is at least partlydetermined by the delivery system. Most silver compounds that dissociatereadily and produce large numbers of free silver ions are highly toxicto mammalian (including human) tissues. Less-toxic compounds, includingsilver sulfadiazine cream (widely used in the treatment of burns) andsilver nitrate solution, do not dissociate readily and therefore do notrelease large numbers of silver ions. These compounds must re reappliedfrequently to maintain their clinical efficacy.

Electrically-generated silver ions, which can penetrate more deeply intothe tissues, are effective even against antibiotic-resistant strains ofbacteria, fingi, etc., inhibiting growth in vivo and in vitro at currentdensities as low as 10 nA/mm² and silver ion concentrations as low as0.5 mg/ml. The effects of electrically generated silver ions aredescribed in a number of publications, including the following: J. A.Spadaro, et al., “Antibacterial Effects of Silver Electrodes with WeakDirect Current,” Antimicrobial Agents & Chemotherapy, Vol. 6, pp.637-642 (1974); T. J. Berger, et. al., “Antifungal Properties ofElectrically Generated Metallic Ions,” Antimicrobial Agents &Chemotherapy, Vol. 10, pp. 856-860 (1976); R. O. Becker, et al.,Treatment of Orthopedic Infections With Electrically-Generated SilverIons,” J. Bone & Joint Surgery, Vol. 60-A, pp. 871-881 (1978)).

Silver and other metals are widely used in wound dressings and metalstherefore. Fabo (U.S. Pat. No. 5,340,363) discloses a dressing thatincludes an outer absorbent layer and an inner porous, hydrophobic layerknitted of elastic threads and encapsulated by a soft, hydrophobicsilicone or polyurethane gel. The gel can be used as a carrier forantibacterial agents such as zinc, pain-relieving substances, and agentsthat stimulate wound repair. Klippel, et al. (U.S. Pat. No. 3,830,908)use micronized allantoin as a carrier for a bactericidal orbacteristatic ingredient (such as silver citro allantoinate) that isdispersed on the surface of a plastic air splint or other bandagingproduct. McKnight, et al. (U.S. Pat. No. 3,800,792) disclose a surgicaldressing having a layer of tanned, reconstituted collagen foam filmlaminated to a thin, continuous layer of an inert polymer. The collagenlayer contains finely-divided silver metal added by soaking the collagenfilm in Tollen's reagent. Stowasser (U.S. Pat. No. 2,934,066) makes adressing of absorbent, metal-coated fibers, such as a carding fleececoated with aluminum and backed by compressed cellulose, and polyamidefibers coated with vacuum deposited silver.

Dressings for provision of electric stimulation are also known. Forexample, Jones (U.S. Pat. No. 4,911,688) covers a wound with a clearcover that serves as a hallow chamber for holding a fluid such as salinein contact with a wound. When connected to a voltage source, a metalanode and a return electrode create free ions and electrical field toenhance healing and tissue regeneration. Juhasz (U.S. Pat. No.4,817,594) discloses a multi-layer dressing for covering discharging,malodorous wounds. The dressing includes a layer of anelectrically-conductive material such as silver and a layer of charcoalfabric. Application of a DC (direct current) voltage to a conductivelayer drives silver ions into the wound to enhance tissue growth andinhibit bacterial growth; application of transcutaneous AC (alternatingcurrent) is used for post-operative pain relief. Seiderman (U.S. Pat.No. 4,767,401) describes a bandage-like device used for iontophoreticadministration of medicaments, including silver-protein colloids. Thedevice includes a metal foil electrode (preferably aluminum), and makesuse of the slight inherent negative electric charge proximate a woundsite to generate a small electric field at the site.

Matson (U.S. Pat. No. 4,728,323) coats a substrate (nylon fabric,polymeric film, fiberglass, gauze, or polyurethane foam) with a film ofa silver salt deposited by vapor or sputter coating techniques.Alternatively, fibers can be coated and then woven or knitted into afabric. Konikoff (U.S. Pat. No. 4,142,521) shows a bandage or surgicalsponge material incorporating one or more electret elements, eachelectret providing a small electrostatic field to the area of the wound.

In application Ser. No. 08/524,134, filed Sep. 5, 1995, Becker, et al.disclose a bimetallic fabric woven of nylon fibers coated with a firstmetal such as silver, interspaced at intervals with fibers coated with asecond metal such as gold or platinum, preferably in a ration of about10:1. Alternatively, deposits of the second metal are placed on a fabricthat contains the first metal. When contacted with an electrolyte, eachcontact junction between the first and second metals serves as abimetallic junction that produces free silver ions. The material may beused in therapeutic or prophylactic treatment of wounds (includingsurgical incisions). An iontophoretic system for promoting tissuehealing processes and inducing regeneration is described in applicationSer. No. 08/623,046, filed Mar. 28, 1996. The system is implemented byplacing a flexible, silver-containing anode in contact with the wound,placing a cathode on intact skin near the anode, and applyingwound-specific DC voltage between the anode and the cathode.Electrically-generated silver ions from the anode penetrate into theadjacent tissues and undergo a sequence of reactions leading toformation of a silver-collagen complex. This complex acts as abiological inducer to cause the formation in vivo of an adequateblastema to support regeneration. The disclosures of theabove-referenced patent applications are incorporated herein byreference.

Regardless of whether silver is provided in the form of silver ions oras a topical composition (silver nitrate solution, silver sulfadiazinecream, etc.), its beneficial effects are manifested primarily at thetreated surface and immediate adjacent tissues, and are limited by theachievable tissue concentration of silver ions. Despite the availabilityof numerous techniques for the delivery of silver and silver compoundsin vitro and in vivo, there remains a need for a delivery system that iscapable of supplying clinically useful concentrations of silver ions toa treatment site without the need for adjuvant electrical stimulation.

SUMMARY OF THE INVENTION

According to its major aspects and broadly stated, the present inventionis a flexible, multilayer dressing for therapeutic and prophylactic use,together with methods for making the dressing. The dressing includes alayer of fabric that contains a metal having bactericidal/bacteristaticproperties, a layer of absorbent material, and, optionally, a layer ofair-permeable and/or water-impermeable material. (For purposes of thisdescription, a metal with “bactericidal properties” and/or“bacteristatic properties” is broadly defined as a metal that is activeagainst at least one type of pathogenic agent, including bacteria,protozoa, fungi, rickettsiae, and viruses. Bactericidal agents killorganisms, whereas bacteristatic agents prevent their growth andmultiplication.)

The multiplayer dressing is used in the care and treatment of skininfections and surface wounds (including surgical incisions), as apacking material for deep wounds, and as a swab for surface cleaning. Inuse, the dressing is effective in preventing the growth of pre-existingbacterial and fungal contaminants (particularly in traumatic wounds),and as a prophylactic measure against airborne contaminants (bacteria,fungi, etc.) and opportunistic infections.

A major feature of the present invention is the inner layer of thedressing, which contacts the wound surface when in use. The inner layercontains a bactericidal/bacteristatic metal preferably silver) looselybound to a flexible, conformable fabric substrate. When the fabric isplaced on the treatment site and contacted by saline, wound exudate, orwater, at least a portion of the metal is released into the surroundingtissues with resulting beneficial effects. The inner layer may be madeof metallized fibers of any suitable material, for example, it may beknitted or woven or silver-coated nylon fibers. Such a fabric isdurable, nontoxic, nonhazardous, and inert until activated by contactwith a suitable liquid.

An important feature of the present invention is the multilayer dressingitself. In a preferred embodiment of the invention, the dressingincludes at least two layers: an inner layer of silver-containing fabricand a layer of moisture-absorbing material. Both layers are sufficientlyflexible to conform to the area being treated, and can be provided insizes and thicknesses suitable for the intended use. In this form, thedressing can be applied to surface wounds such as cuts (includingsurgical incisions), scrapes, and burns. It can also be applied tointact skin to treat localized infections, or used to pack deep woundcavities. For surface applications, the multilayer material may includea third, outer layer or an air-permeable and/or water impermeablematerial. If desired, a layer of a suitable adhesive can be added toadhere the dressing to the skin.

Another feature of the present invention is the method for making thedressing, which can be adapted for a variety of end uses. The dressingmay be made by any convenient techniques known in the art, of readilyavailable, generally inexpensive materials. It may be provided in aconvenient form for a variety of applications, ranging from individualBAND-AID®-type dressings to rolls or sheets that can be cut to anyneeded size. For example, a two-layer dressing approximately 4″ wide and3′, long (about 10×90 cm), wherein the absorbent layer is no more than2-3 times as thick as the silver fabric layer, is useful for packingdeep wound cavities. On the other hand, a three-layer dressing with anair-permeable outer layer may be preferred for a burn or surgicalincision.

Other features and advantages of the present invention will be apparentto those skilled in the art from a careful reading of the DetailedDescription of a Preferred Embodiment presented below and accompanied bythe drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings,

FIG. 1 is a cross-sectional view of a multilayer dressing according to apreferred embodiment of the present invention;

FIG. 2 is a cross-sectional view of a multilayer dressing according toanother preferred embodiment of the invention;

FIG. 3 is a perspective view of the multilayer dressing of FIG. 2, shownpacked in a dispenser;

FIG. 4 is a perspective view of another multilayer dressing according tothe invention; and

FIGS. 5-7 are plan views of additional multilayer dressings according tothe invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

In the following detailed description, reference numerals are used toidentify structural elements, portions of elements, surfaces and areasin the drawings. For consistency, whenever the same numeral is used indifferent drawings, it indicates the same element, portion, surface andarea as when first used.

Referring now to FIG. 1, there is shown a cross-sectional view of amultilayer material 10 according to a preferred embodiment of thepresent invention. Multilayer material 10 includes a first layer 12 of asilver-containing fabric and a second layer 14 of a moisture-absorbentmaterial.

First layer 12 consists of a flexible, conformable metallized fabricmade by weaving, knitting, crocheting, felting, blowing, or some otherconvenient process. Preferably, first layer 12 is made of silver-coatednylon fibers. However, other materials may also be suitable, includingnonwoven sheet material that incorporate or are coated with suitableamounts of silver.

Silver (or some other metal with medically usefulbactericidal/bacteristatic properties) may be added to the fibers oflayer 12 by vapor coating, aerosolized deposition, sputter coating orother standard techniques known in the art. Individual fibers can becoated and then worked (woven, knitted, crocheted, felted, blown, etc.)into fabric. Alternatively, suitable amounts of silver may be added tothe finished fabric. While the thickness of such a silver coating mayvary broadly, the amount of silver should be such that layer 12 has aspecific resistance no greater than approximately 5 Ω/cm; mostpreferably, layer 12 has a specific resistance no greater thanapproximately 1 Ω/cm. Typically, a medically-useful material for layer12 contains at least approximately 5 wt. % silver, preferablyapproximately 20 wt. % silver. However, the metal content and specificresistance of layer 12, as well as the thickness and uniformity of thecoating, may vary broadly depending on the selected metal and theintended uses of dressing 10. Thus, fabrics with lesser amounts of metalmay also be useful in the practice of the invention. Materials withhigher resistance (and lower silver content) may also be useful;however, such materials will generally be incapable of supplying theneeded amounts of free silver to the treatment site.

Layer 12 should also not only be made of a material having asufficiently high content of silver (or other suitable metal), but thesilver should be approximately uniformly distributed. Non-uniformdistribution means that the wound will not be uniformly treated: theamount of silver supplied to different areas will differ.

The silver in layer 12 is releasably attached to the fabric substrate sothat, when layer 12 is placed in contact with body tissues and moistenedby a suitable liquid, at least a portion of the silver migrates into theadjacent tissues. While not wishing to be bound by theory, it isbelieved that metallized fabrics wherein the metal atoms are somewhatloosely bound to the molecules of the fabric substrate (forming achemical or physical complex with the substrate rather than being simplydeposited onto it) are especially suitable for the practice of thepresent invention. In a complex of this nature, the bond energy issufficiently low to permit effusion of the metal when the fabric is wet.

Second layer 14 is made of a soft, flexible, moisture-absorbent materialcapable of seeping up wound exudates, such as woven or nonwoven cotton(layer 14 may be moistened with water, normal saline, or other suitableliquid when dressing 10 is in use). Layer 14 need be no more thanapproximately 0.1-0.5 cm thick; however thicker layers may be usefulwhen material 10 is used in the care of draining wounds.

Multilayer material 10 is inert until moistened by water, wound exudate,normal saline, or other liquid. Then, the bonds between the silver atomsand the fabric substrate of first layer 12 are loosened and at leastsome of the silver migrates from the fabric into the surroundingtissues. When placed on a wound with first layer 12 contacting the bodysurface, naturally-occurring body fluids may be sufficient to activatematerial 10. However, a suitable liquid (normal saline, Ringer'ssolution, tap water and the like) must generally be applied to ensurerelease of silver from layer 12.

Another multilayer material according to the present invention is shownin FIG. 2. A material 20, like above-described material 10, includes ametal-containing layer 12 and a moisture-absorbing layer 14. Adjacent tolayer 14 is a thin, flexible outer layer 16 made of nonporous plasticmaterial, with a plurality of perforations 18 therethrough. Outer layer16 may be made of an air-permeable, moisture-impermeable material suchas GORETEX®. Alternatively, layer 16 may be a plastic material such asthe materials used in commercially-available dressings (BAND-AID®,CURAD®, etc.)

Materials 10 and 20 may be finished in dimensions to suit variousapplications, for example, 2″ (about 5 cm) widths for covering surgicalincisions and relatively small wounds, and 12″ (about 30 cm) or largerwidths for covering large wounds such as burns, and cut to any neededlength. When made in sections approximately 4″×3′ (about 10×90 cm) andwith an absorbent layer 14 no thicker than approximately 2-3 times thethickness of layer 12, material 10 is useful as a packing material fordeep wounds. Material 20 (or material 10) may be packed in a dispenser22 for shipping, storage, and eventual use (FIG. 3).

Materials 10 and 20 may be used in a variety of wound dressings toprovide prophylactic and/or therapeutic activity to help prevent (ortreat) infection and facilitate healing. The dimensions andconfiguration of such dressings depend on the size and location of thearea to be treated, and requires a means for affixing the dressing inplace, controlling moisture loss from the wound, and ensuring directcontact between the layer 12 and the actual wound surface itself.

A wound dressing 30 according to the present invention is shown in FIG.4. Dressing 30 includes a thin, flexible outer layer 16, an absorbentlayer 14 attached to the medial portion of layer 16, and at least oneinner layer 12 of silver-containing fabric (layers 12 and 14 are shownpulled away from layer 16 for clarity). Perforations (18) in the medicalportion of layer 16 provide added ventilation of the wound surface toassist in epitheliazation. An inner side 34 of layer 16, on either sideof layers 12, 14, may be coated with adhesive and protected with aremovable strip of material (not shown) that is peeled off just prior touse. Dressing 30 is flexible and, via the adhesive coating on layer 32,capable of adhering to dry skin. In use, wound exudate (or some otherliquid) moistens layer 12 and passes therethrough to absorbent,moisture-retaining layer 14.

Another wound dressing 40 is shown in FIG. 5. Dressing 40 is made ofmaterial 20, thus, includes a silver-containing layer 12, an absorbentlayer 14 (not shown), and an outer layer 16 having a larger area thanlayer 12. A layer of adhesive 36 coats the inner side of layer 16,generally as shown. A dressing 42 with adhesive margins 36 may befurnished in a strip of any convenient length (FIG. 6). Adhesive 36 maybe covered by a peel-off strip (not shown) prior to use. Dressings 40,42 may, of course, be made in any convenient sizes.

A wound dressing 50 adapted for placement on fingertip wounds is shownin FIG. 7. Dressing 50, like dressing 40, is made of material 20 and hasan outer layer 16 that is larger in area than silver-containing layer 12and a layer of adhesive 36 coating the inner side of layer 16. Aplurality of radial slits 52 extend inwards from the periphery ofdressing 50, to form a series of flaps 54 about a central portion 56.Dressing 50 preferably has at least four slits 52 forming four flaps 54.However, a greater number of slits 52, such as the twelve slits 52 atapproximately 30° intervals shown in FIG. 7, are preferred.

In use, portion 56 is centered on the fingertip with layer 12 adjacentto the skin. Flaps 54 are affixed to the skin by adhesive 36, distal towound. By overlapping flaps 54, the user can form dressing 50 into a“cap” that covers the fingertip. While human digits vary widely in size,a dressing 50 approximately 2″ (about 5 cm) in diameter with a centralportion 56 approximately 1″ (about 2.5 cm) in diameter is suitable formost. However, dressing 50 can easily be made in different sizes tobetter fit very small or very large digits.

Multilayer materials 10, 20 (and dressings made with the materials) areflexible, easily re-shapeable and conformable to the region to betreated. Materials 10, 20 can be used for treating surface wounds suchas cuts, scrapes, and burns, and also be used for filling in deep woundcavities, thereby enabling the wound edges to be kept apart during thehealing process.

In use, materials 10, 20 (or dressings such as dressings 30, 40, 42, 50)are applied to the skin after appropriate surface preparation (dressings30, 40, 42 are preferably applied to dry skin so that adhesive 36adheres well to the skin to hold the dressing in place). Depending onthe area to be treated, the layers 12, 14 may be moistened to stimulaterelease of silver from the material. Silver is released from layer 12and migrates into the area to minimize external and cross-contaminationof the treatment site, and help prevent bacterial and fungal infections,while not hindering normal cell growth or repair. No toxic substance isintroduced into the patient's body. Materials 10, 20 (and dressings thatcontain these materials) are preferably replaced daily; however, thematerials can be safely left in place for as long as 3 days ifcircumstances so require. The materials can be used for prophylactictreatment of fresh wounds and surgical incisions, treatment orprevention of early stage decubital ulcers (“bed sores”), therapeutictreatment of infected and traumatic wounds, and so forth.

The present invention is further illustrated in the followingnonlimiting examples.

EXAMPLE 1

The effectiveness of warp knit silver nylon fabric (specific resistanceabout 1 Ω/cm) in inhibiting the growth of three common strains ofbacteria (S. aureus, E. coli and P. aeuginosa) was tested in vitro. Thebacterial cultures were planted in agar-filled petri dishes using theKirby Bauer technique, one culture per dish. Sterilized 1-cm squares ofthe fabric were placed on the surfaces of the cultures. Everytwenty-four hours, each fabric square was removed from the culturemedium and replanted in a different area of the same dish. After 72hours, the culture medium directly underneath the fabric squares wasclear (i.e., the bacteria in those regions had been killed). Inaddition, all areas where the fabric squares had been placed previouslyremained clear.

EXAMPLE 2

The warp knit silver nylon fabric of Example 1 was found to causededifferentiation of mammalian cell in vitro. The observed effects wereproportional to the concentration of silver ions in the culture mediumand inversely proportional to distance from the fabric: the closer tothe fabric, the greater the concentration of dedifferentiated cells andthe greater the silver ion concentration.

EXAMPLE 3

The effectiveness of silver sulfadiazine cream, silver nylon fabric, andplain nylon fabric in inhibiting the bacterial growth was compared (L.Smee, “The Effectiveness of Silver Nylon Cloth and Silver SulfadiazineCream as Antiseptics,” Piedmont College Senior Thesis, April, 1996).Five common strains of bacteria were studied including two gram-negativestrains (E. coli, P. aeruginosa) and three gram-positive strains (E.faecalis, S. aureus, S. pyogenes).

Each strain of bacterium was inoculated into three agar-filled petridishes. Following the inoculation, three fabric disks were placed intoeach dish: a disk of plain nylon cloth which served as a control, a diskof silver nylon fabric, and a plain nylon disk which has been coatedwith silver sulfadiazine cream. Each disk had a surface area of 3.4 mm².The dishes were incubated for seventy-two hours, and removed everytwenty-four hours to measure the inhibition zone around each disk (i.e.,the distance from the outer edge of the fabric disk to the perimeter ofthe clear zone of the inhibited bacterial growth about the disk).

Results indicated that the silver nylon fabric and silver sulfadiazinecream were effective bacterial grown inhibitors against all testedstrains. Average results for two trials are listed in Table I.

TABLE I Inhibition zones (mm) for silver nylon fabric (Ag Nylon), nylonfabric with silver sulfadiazine cream (Nylon + Ag Cream), and plainnylon fabric (Nylon). Results shown represent the average of two trials.Ag Nylon Nylon + Ag Cream Nylon E. coli Day 1 7.4 6.3 -0- Day 2 9.2 6.4-0- Day 3 10 7.2 -0- P. aeruginosa Day 1 57 32 -0- Day 2 59 29 -0- Day 362 29 -0- E. faecalis Day 1 8.9 4.0 -0- Day 2 11 3.8 -0- Day 3 15 2.4-0- S. aureus Day 1 9.3 7.1 -0- Day 2 9.5 2.1 -0- Day 3 12 0.9 -0- S.pyogenes Day 1 57 28 -0- Day 2 66 34 -0- Day 3 70 38 -0-

These results indicate that silver nylon fabric is an effectiveantimicrobial agents. In Example 3, the fabric proved to be moreeffective than silver sulfadiazine cream, creating and maintaining alarger inhibition zone for each strain tested for the duration of theexperiments.

As a delivery system for silver, a fabric with a sufficiently highconcentration of silver releases silver ions at a steady rate for aslong as the fabric is in contact with the culture medium (in vitro or invivo). Such a fabric does not cause allergic reactions, thus, its useprevents other potentially-harmful side effects associated with otherdelivery systems (silver sulfadiazine, silver thiosulfate). A multilayerdressing using the fabric is nonhazardous, conformable to the shape ofthe site to be treated, readily adaptable to diverse clinicalsituations, and safe and easy to use. When treating patients withextensive burns, a dressing according to the invention is lessexpensive, less cumbersome, and more effective than silver sulfadiazinecream.

It will be apparent to those skilled in the art that many changes andsubstitutions can be made to the preferred embodiment herein describedwithout departing from the spirit and scope of the present invention asdefined by the appended claims.

1. A wound dressing, comprising: a flexible, conformable fabric substrate comprising an effective amount of silver-coated fibers worked into or forming the flexible, conformable fabric substrate to passively release an effective amount of silver from the wound dressing into a wound at a steady rate for as long as three days when the wound dressing contacts saline, wound exudate or water at the wound, wherein the flexible, conformable fabric substrate has a specific resistance no greater than approximately 5 μ/cm.
 2. The wound dressing of claim 1, wherein the flexible, conformable fabric substrate comprises at least approximately 5 wt. % silver.
 3. The wound dressing of claim 1, wherein the flexible, conformable fabric substrate comprises at least approximately 20 wt. % silver.
 4. The wound dressing of claim 1, wherein the flexible, conformable fabric substrate has a specific resistance no greater than approximately 1 Ω/cm.
 5. The wound dressing of claim 1, wherein the silver is loosely bound to the plurality of fibers.
 6. The wound dressing of claim 1, wherein the wound is a traumatic wound.
 7. The wound dressing of claim 6, wherein the traumatic wound is a decubital ulcer.
 8. A wound dressing, comprising: a flexible fabric substrate comprising silver-coated fibers; and a layer of moisture-absorbing material attached to said substrate, wherein the silver and the substrate have a combined weight, wherein the quantity of silver is at least approximately 5 wt. % of the combined weight, and wherein an effective amount of silver is passively released at a steady rate for as long as three days at a treatment site from the wound dressing without application of an electric current when the wound dressing contacts saline, wound exudate or water at the treatment site.
 9. The wound dressing of claim 8, wherein the silver and the substrate have a combined weight, and wherein the silver is at least approximately 20 wt. % of said combined weight.
 10. The wound dressing of claim 8, wherein the fibers are nylon.
 11. The wound dressing of claim 8, further comprising a third layer adjacent to said layer of moisture-absorbing material, said third layer made of water-impermeable material.
 12. The wound dressing of claim 8, further comprising a third layer adjacent to said layer of moisture-absorbing material, said third layer made of an air-permeable material.
 13. The wound dressing of claim 8, wherein said moisture-absorbing material is made of cotton.
 14. The wound dressing of claim 8, further comprising an adhesive layer attached to at least a portion of said moisture-absorbing material said for adhering said dressing to intact skin.
 15. The dressing as recited in claim 8, further comprising: a third layer adjacent to said layer of moisture-absorbing material, said third layer made of a water-impermeable material; and an adhesive carried by at least a portion of said third layer, said adhesive positioned so that said adhesive adheres to intact skin when said dressing is placed in contact with a wound.
 16. The wound dressing of claim 8, wherein the moisture-absorbing material absorbs wound exudate through the fabric substrate. 